Some projection display apparatuses (projectors) have a function for keystone correction (trapezoidal distortion correction). The keystone correction includes vertical keystone correction, as correction in the top and bottom direction, and horizontal keystone correction, as correction in the right and left direction. The projection display apparatuses having the keystone correction function include a manual type which is provided with two discrete rotary knobs to adjust the amount of vertical keystone correction and the amount of horizontal keystone correction in accordance with rotations of the rotary knobs (refer to PTL 1, for example).